WO1995027627A1 - Method for making a code image, original comprising such a code image and photocopier for copying such an original - Google Patents

Method for making a code image, original comprising such a code image and photocopier for copying such an original Download PDF

Info

Publication number
WO1995027627A1
WO1995027627A1 PCT/NL1994/000072 NL9400072W WO9527627A1 WO 1995027627 A1 WO1995027627 A1 WO 1995027627A1 NL 9400072 W NL9400072 W NL 9400072W WO 9527627 A1 WO9527627 A1 WO 9527627A1
Authority
WO
WIPO (PCT)
Prior art keywords
code image
fourier transform
picture
photocopier
original
Prior art date
Application number
PCT/NL1994/000072
Other languages
French (fr)
Inventor
Sijbrand Spannenburg
Original Assignee
Joh. Enschedé En Zonen Grafische Inrichting B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to NL9201701A priority Critical patent/NL194267C/en
Priority claimed from NL9201701A external-priority patent/NL194267C/en
Application filed by Joh. Enschedé En Zonen Grafische Inrichting B.V. filed Critical Joh. Enschedé En Zonen Grafische Inrichting B.V.
Priority to PCT/NL1994/000072 priority patent/WO1995027627A1/en
Priority to AU65452/94A priority patent/AU6545294A/en
Publication of WO1995027627A1 publication Critical patent/WO1995027627A1/en

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/00838—Preventing unauthorised reproduction
    • H04N1/0084—Determining the necessity for prevention
    • H04N1/00843—Determining the necessity for prevention based on recognising a copy prohibited original, e.g. a banknote
    • H04N1/00846—Determining the necessity for prevention based on recognising a copy prohibited original, e.g. a banknote based on detection of a dedicated indication, e.g. marks or the like
    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/004—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using digital security elements, e.g. information coded on a magnetic thread or strip
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
    • B42D25/29—Securities; Bank notes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/00838—Preventing unauthorised reproduction
    • H04N1/00856—Preventive measures
    • H04N1/00859—Issuing an alarm or the like
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/00838—Preventing unauthorised reproduction
    • H04N1/00856—Preventive measures
    • H04N1/00864—Modifying the reproduction, e.g. outputting a modified copy of a scanned original
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/00838—Preventing unauthorised reproduction
    • H04N1/00856—Preventive measures
    • H04N1/00875—Inhibiting reproduction, e.g. by disabling reading or reproduction apparatus
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/00838—Preventing unauthorised reproduction
    • H04N1/00883—Auto-copy-preventive originals, i.e. originals that are designed not to allow faithful reproduction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
    • H04N2201/3201—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
    • H04N2201/3269—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title of machine readable codes or marks, e.g. bar codes or glyphs
    • H04N2201/327—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title of machine readable codes or marks, e.g. bar codes or glyphs which are undetectable to the naked eye, e.g. embedded codes

Definitions

  • the invention relates to a method for making a code image from a picture, said code image being detectable by a photocopier with a sampling frequency.
  • the invention also relates to an original comprising a code image detectable by a photocopier with a sampling frequency and to a photocopier with a sampling frequency for copying an original comprising a code image, the photocopier having a detection apparatus for detecting the code image.
  • Dutch patent application 90.02740 dis ⁇ closes providing the original with a copy security element in the form of a grid angle modulated code image which is detectable by a photocopier.
  • this grid angle modulated code image prevents unauthorized copying with a fair amount of success, effective operation can be nega ⁇ tively influenced by the use of digital filters or other image correcting techniques. The need for other security elements is thus still present. It is among other things an object of the present inven ⁇ tion to provide an alternative code image which is at least substantially imperceptible by the human visual system, but which can easily be detected by (in particular digital) photocopiers.
  • a method of the sort named in the intro ⁇ ductory part is characterized according to the invention in that the method comprises the following steps: - determining the Fourier transform of the picture,
  • the invention is based on the insight that for the graphic reproduction of images on a substrate, for example paper, only a small part of the total information capacity of this substrate is used.
  • the human visual system can per ⁇ ceive frequencies of up to approximately 50 periods per degree, which corresponds to approximately 10 periods per millimetre on the substrate at an assessment distance of 30 cm.
  • present-day digital photocopiers scan an original at a higher frequency of, for example, 400 dpi or 16 periods per millimetre.
  • This frequency band (also called sampling band) is thus outside the band width of the human visual system and can be considered to be a side band which can serve as 'carrier wave' for information which is beyond the assessment range of the human visual system.
  • the invention makes use of this by removing almost all frequency components from the information on the picture carrier which are in the low frequency bands visible to the human eye.
  • the remaining frequency compo ⁇ nents appear to give a digital photocopier sufficient information to reconstruct the picture and make it visible again to the human eye.
  • the inventive method (also called SABIC: Sample-Band Image Coding) is based, among other things, on the Sampling theorem which applies to sampling images by digital photo ⁇ copiers. This theorem postulates that if an image is sampled with a frequency which is higher than twice the highest frequency which occurs in the image, that image can be reconstructed completely from the samples. If, however, the sampling frequency is too low then the so-called aliasing effect occurs. That means that for fre ⁇ quencies in the image which are under half of the sampling frequency, in other words the remaining frequency compo ⁇ nents, it holds that these frequencies, when sampled thus when copied, are mirrored about the axis of half the sampling frequency.
  • the invention provides an original pro ⁇ tected against unauthorized copying comprising a code image detectable by a photocopier with a sampling fre ⁇ quency, which original is characterized in that the code image is formed by the inverse Fourier transform of a processed Fourier transform of a picture, the processed Fourier transform of the picture being the Fourier trans ⁇ form of the picture from which all frequency components larger than half the sampling frequency have been removed and the remaining frequency components being mirrored about the axes which correspond to half of the sampling frequency.
  • Such a code image applied to the original is not visible to the human eye but appears on the copy after the copying process. By so doing the copy is distinguishable from the original.
  • a photocopier should preferably be provided with a detection apparatus for detecting the inventive code image in order to prevent unauthorized copying.
  • the detection apparatus recog ⁇ nizes a code image in the original, then, preferably by means of an inhibition circuit, copying is made impos ⁇ sible.
  • a digital photocopier can be produced in such a way that originals with an inventive code image cannot be copied.
  • Fig. 1 shows a picture which is to be made into a code image
  • Fig. 2 shows the amplitude of the Fourier transform of figure 1
  • Fig. 3 shows the phase of the Fourier transform of figure
  • Fig. 4 shows the amplitude according to figure 2 after the inventive process
  • Fig. 5 shows the phase according to figure 3 after the inventive process
  • Fig. 6 shows the inverse Fourier transform
  • the code image of figures 4 and 5
  • Fig. 7 shows a copy of figure 6 by means of a digital photocopier
  • Fig. 8 shows an original
  • Fig. 9 shows the original of figure 8 with the code image of figure 6 superimposed thereon
  • Fig. 10 shows a copy of figure 9 by means of a digital photocopier
  • Fig. 11 shows the picture of figure 9 after processing by a low-pass filter
  • Fig. 12 shows the picture of figure 9 after processing by a high-pass filter
  • Fig. 13 shows a copy of figure 12 by means of a digital photocopier.
  • FIG l an arbitrary picture is shown which is to be converted by means of the method accprding to the inven ⁇ tion into a code image detectable by a photocopier with a sampling frequency.
  • the Fourier trans ⁇ form of this picture is determined as follows. The picture is discreted by determining the grey values of each pic ⁇ ture element. This determination of the grey values can be done by measuring light reflected by the picture element. Thus a two dimensional function of grey values is obtained, w...ich is subjected to a discrete two dimensional Fourier transformation, for example a Fast Fourier Trans ⁇ form algorithm. The amplitude of the Fourier transform of the picture and the phase thereof are shown in figures 2 and 3 respectively.
  • this original is provided preferably over the whole surface with a code image as shown in figure 6.
  • Figure 9 shows the original with the superimposed code image. If a copy is made of that original with code image (figure 10) then the picture reappears, as a result of which the copy becomes useless.
  • Figure 11 thus shows the result after using a digital low-pass filter and figure 12 the result after using a high-pass filter.
  • the sampling, that is the copying, of the code image of figure 12 with the correct frequency allows the original picture to return.

Abstract

Method for making a code image from a picture, said code image being detectable by a photocopier with a sampling frequency. In the method, the Fourier transform of the picture is determined, all frequency components larger than half of the sampling frequency are removed from the Fourier transform, the remaining frequency components of the Fourier transform are mirrored about the axes which correspond to half of the sampling frequency, and the inverse Fourier transformation is applied hereto. An original provided with such a code image offers a security against copying up to a certain point and can be detected by a detection apparatus of a photocopier.

Description

Method for making a code image, original comprising such a code image and photocopier for copying such an original
The invention relates to a method for making a code image from a picture, said code image being detectable by a photocopier with a sampling frequency.
The invention also relates to an original comprising a code image detectable by a photocopier with a sampling frequency and to a photocopier with a sampling frequency for copying an original comprising a code image, the photocopier having a detection apparatus for detecting the code image.
Now that advanced photocopiers, among them in particular colour photocopiers with array laser scanning and graphic format stations, have become available to a large public, nowadays large numbers of copies of an original can be cheaply and speedily obtained, the copies being completely or almost completely indistinguishable from the original.
In order to prevent unauthorized copying of originals, such as securities, for example bank notes, or confiden¬ tial documents, Dutch patent application 90.02740 dis¬ closes providing the original with a copy security element in the form of a grid angle modulated code image which is detectable by a photocopier. Although this grid angle modulated code image prevents unauthorized copying with a fair amount of success, effective operation can be nega¬ tively influenced by the use of digital filters or other image correcting techniques. The need for other security elements is thus still present. It is among other things an object of the present inven¬ tion to provide an alternative code image which is at least substantially imperceptible by the human visual system, but which can easily be detected by (in particular digital) photocopiers.
For this purpose a method of the sort named in the intro¬ ductory part is characterized according to the invention in that the method comprises the following steps: - determining the Fourier transform of the picture,
- removing all frequency components larger than half of the sampling frequency from the Fourier-transform,
- mirroring the remaining frequency components of the Fourier transform about the axes which correspond to half of the sampling frequency, and
- applying the inverse Fourier transformation hereto.
The invention is based on the insight that for the graphic reproduction of images on a substrate, for example paper, only a small part of the total information capacity of this substrate is used. The human visual system can per¬ ceive frequencies of up to approximately 50 periods per degree, which corresponds to approximately 10 periods per millimetre on the substrate at an assessment distance of 30 cm. However, present-day digital photocopiers scan an original at a higher frequency of, for example, 400 dpi or 16 periods per millimetre. This frequency band (also called sampling band) is thus outside the band width of the human visual system and can be considered to be a side band which can serve as 'carrier wave' for information which is beyond the assessment range of the human visual system. The invention makes use of this by removing almost all frequency components from the information on the picture carrier which are in the low frequency bands visible to the human eye. The remaining frequency compo¬ nents appear to give a digital photocopier sufficient information to reconstruct the picture and make it visible again to the human eye.
After extensive research within the theory of signal processing there it was found that removing those fre- quency components from the picture which are visible to the human eye, whilst the picture can still be 'seen' by a digital photocopier can take place by means of the inven¬ tive method.
The inventive method (also called SABIC: Sample-Band Image Coding) is based, among other things, on the Sampling theorem which applies to sampling images by digital photo¬ copiers. This theorem postulates that if an image is sampled with a frequency which is higher than twice the highest frequency which occurs in the image, that image can be reconstructed completely from the samples. If, however, the sampling frequency is too low then the so- called aliasing effect occurs. That means that for fre¬ quencies in the image which are under half of the sampling frequency, in other words the remaining frequency compo¬ nents, it holds that these frequencies, when sampled thus when copied, are mirrored about the axis of half the sampling frequency.
This explains why in the inventive method the frequency components above half of the sampling frequency are removed and are mirrored about the axes which correspond to half of the sampling frequency.
At the same time the invention provides an original pro¬ tected against unauthorized copying comprising a code image detectable by a photocopier with a sampling fre¬ quency, which original is characterized in that the code image is formed by the inverse Fourier transform of a processed Fourier transform of a picture, the processed Fourier transform of the picture being the Fourier trans¬ form of the picture from which all frequency components larger than half the sampling frequency have been removed and the remaining frequency components being mirrored about the axes which correspond to half of the sampling frequency.
Such a code image applied to the original is not visible to the human eye but appears on the copy after the copying process. By so doing the copy is distinguishable from the original.
As an original image with a code image obtained by the invention and overlayed thereon can be separated by means of digital high-pass and low-pass filters, a photocopier should preferably be provided with a detection apparatus for detecting the inventive code image in order to prevent unauthorized copying. When the detection apparatus recog¬ nizes a code image in the original, then, preferably by means of an inhibition circuit, copying is made impos¬ sible. Thus a digital photocopier can be produced in such a way that originals with an inventive code image cannot be copied.
Some embodiments of the invention will hereinafter be described in more detail with reference to the drawing. In the drawings
Fig. 1 shows a picture which is to be made into a code image,
Fig. 2 shows the amplitude of the Fourier transform of figure 1, Fig. 3 shows the phase of the Fourier transform of figure
1,
Fig. 4 shows the amplitude according to figure 2 after the inventive process,
Fig. 5 shows the phase according to figure 3 after the inventive process,
Fig. 6 shows the inverse Fourier transform, the code image, of figures 4 and 5, Fig. 7 shows a copy of figure 6 by means of a digital photocopier,
Fig. 8 shows an original,
Fig. 9 shows the original of figure 8 with the code image of figure 6 superimposed thereon,
Fig. 10 shows a copy of figure 9 by means of a digital photocopier,
Fig. 11 shows the picture of figure 9 after processing by a low-pass filter, Fig. 12 shows the picture of figure 9 after processing by a high-pass filter,
Fig. 13 shows a copy of figure 12 by means of a digital photocopier.
In order to let the description be as clear as possible, all the pictures represented in the figures have been represented about five times the full size. Apart from that all figures have been executed with a resolution of 512 x 512 picture elements, which in general deviates from the resolution used in practice.
In figure l an arbitrary picture is shown which is to be converted by means of the method accprding to the inven¬ tion into a code image detectable by a photocopier with a sampling frequency. In this embodiment the Fourier trans¬ form of this picture is determined as follows. The picture is discreted by determining the grey values of each pic¬ ture element. This determination of the grey values can be done by measuring light reflected by the picture element. Thus a two dimensional function of grey values is obtained, w...ich is subjected to a discrete two dimensional Fourier transformation, for example a Fast Fourier Trans¬ form algorithm. The amplitude of the Fourier transform of the picture and the phase thereof are shown in figures 2 and 3 respectively. Then the frequencies which are larger than half of the sampling frequency are filtered out of this amplitude and phase, and the frequencies which are smaller than half of the sampling frequency are mirrored about axes which correspond to half the sampling fre¬ quency. The resulting processed amplitude and phase Fourier transforms are shown in figures 4 and 5 respect- ively.
The inverse Fourier transform, which is shown in figure 6, and which forms the code image is then determined from these two pictures. In this code image all information which was also visible to the human eye, that is which was in a low frequency band, is transferred to a high fre¬ quency band and because of this is then no longer visually perceptible. Sufficient information remains, however, for a digital photocopier to reconstruct the picture. This is shown in figure 7. Figure 7 shows the code image of figure 6 which has been sampled, that is copied, with the cor¬ rect frequency and phase (in this example with a reso¬ lution of 128 x 128 picture elements) .
As the sampling frequency of the photocopier is not larger than twice the highest frequency in the code image, with frequencies between a half and a whole sampling frequency, an under-sampling occurs. As a result, of this under-samp¬ ling a new mirroring of the frequencies about axes with half the sampling frequencies occurs, as a result of which the frequencies come into a lower frequency band and are thus visible to the human eye.
In order to secure an original against unauthorized copy- ing, as is shown for example in figure 8, this original is provided preferably over the whole surface with a code image as shown in figure 6. Figure 9 shows the original with the superimposed code image. If a copy is made of that original with code image (figure 10) then the picture reappears, as a result of which the copy becomes useless.
Although this offers a security up to a certain point, the the two superimposed pictures can be separated from one another by means of proper use of digital low-pass and high-pass filters which are a standard feature in digital photocopiers, by which means unauthorized copying could still be possible. Figure 11 thus shows the result after using a digital low-pass filter and figure 12 the result after using a high-pass filter. The sampling, that is the copying, of the code image of figure 12 with the correct frequency allows the original picture to return. By pro- viding photocopiers according to the invention with a detection apparatus for detecting a code image, it is possible to take certain measures when a code image is detected. Thus the detection apparatus preferably contains an inhibition circuit, which inhibits every copying act- ivity when detecting a code image. Alternatively, in the case of positive detection deformations can be introduced in the copy or a quiet alarm can be sounded.
AS/FL

Claims

C L A I M S
1. Method for making a code image from a picture, said code image being detectable by a photocopier with a sam¬ pling frequency, characterized in that the method com¬ prises the following steps: - determining the Fourier transform of the picture,
- removing all frequency components larger than half of the sampling frequency from the Fourier transform,
- mirroring the remaining frequency components of the Fourier transform about the axes which correspond to half of the sampling frequency, and
- applying the inverse Fourier transformation hereto.
2. Original comprising a code image detectable by a photo¬ copier with a sampling frequency, characterized in that the code image is formed by the inverse Fourier transform of a processed Fourier transform of a picture, the proces¬ sed Fourier transform of the picture being the Fourier transform of the picture from which all frequency compo¬ nents larger than half the sampling frequency have been removed and the remaining frequency components being mirrored about the axes which correspond to half of the sampling frequency.
3. Photocopier with a sampling frequency for copying an original comprising a code image, the photocopier having a detection apparatus for detecting the code image, charac¬ terized in that the detection apparatus is suitable for detecting a code image which is formed by the inverse Fourier transform of a processed Fourier transform of a picture, the processed Fourier transform of the picture being that Fourier transform of the picture from which all frequency components larger than half of the sampling frequency have been removed and the remaining frequency components being mirrored about the axes which correspond to half of the sampling frequency.
4. Photocopier according to claim 3, characterized in that the detection apparatus contains an inhibition circuit.
PCT/NL1994/000072 1992-10-01 1994-04-08 Method for making a code image, original comprising such a code image and photocopier for copying such an original WO1995027627A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
NL9201701A NL194267C (en) 1992-10-01 1992-10-01 Method for manufacturing a code image, original provided with such a code image and copying machine for copying such an original.
PCT/NL1994/000072 WO1995027627A1 (en) 1992-10-01 1994-04-08 Method for making a code image, original comprising such a code image and photocopier for copying such an original
AU65452/94A AU6545294A (en) 1992-10-01 1994-04-08 Method for making a code image, original comprising such a code image and photocopier for copying such an original

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL9201701A NL194267C (en) 1992-10-01 1992-10-01 Method for manufacturing a code image, original provided with such a code image and copying machine for copying such an original.
PCT/NL1994/000072 WO1995027627A1 (en) 1992-10-01 1994-04-08 Method for making a code image, original comprising such a code image and photocopier for copying such an original

Publications (1)

Publication Number Publication Date
WO1995027627A1 true WO1995027627A1 (en) 1995-10-19

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Cited By (7)

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Publication number Priority date Publication date Assignee Title
WO1997001832A1 (en) * 1995-06-27 1997-01-16 Mikoh Technology Limited A method of reproducing information
EP0855829A2 (en) * 1997-01-24 1998-07-29 NOKIA TECHNOLOGY GmbH Hiding an authentication code in an electric signal
NL1006937C2 (en) * 1997-09-04 1999-03-05 Oce Tech Bv Resolution increase by synthesis of scan signals.
US6351537B1 (en) 1998-10-05 2002-02-26 3M Innovative Properties Company Verifiable holographic article
NL1017173C2 (en) 2001-01-23 2002-08-14 Joh Enschedu B V Security image with double band encryption.
US6678392B2 (en) * 1992-07-31 2004-01-13 Digimarc Corporation Method for encoding auxiliary data within a source signal
EP1435547A1 (en) * 2001-10-11 2004-07-07 Dai Nippon Printing Co., Ltd. Optical structure body for authentication, recording medium for authentication, and confirmation method

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EP0382549A2 (en) * 1989-02-10 1990-08-16 Canon Kabushiki Kaisha Apparatus for image reading or processing
EP0490457A1 (en) * 1990-12-13 1992-06-17 Joh. Enschedé en Zonen Grafische Inrichting B.V. Support provided with a security element
WO1993025038A1 (en) * 1992-05-29 1993-12-09 Ecole Polytechnique Federale De Lausanne (Epfl) Method for the marking of documents
NL9201701A (en) * 1992-10-01 1994-05-02 Enschede & Zonen Grafisch Security system to detect photocopying of e.g. banknotes

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2217258A (en) * 1988-03-24 1989-10-25 Suomen Pankin Setelipaino A security document with a warning pattern and a method for the preparation thereof
EP0382549A2 (en) * 1989-02-10 1990-08-16 Canon Kabushiki Kaisha Apparatus for image reading or processing
EP0490457A1 (en) * 1990-12-13 1992-06-17 Joh. Enschedé en Zonen Grafische Inrichting B.V. Support provided with a security element
NL9002740A (en) * 1990-12-13 1992-07-01 Enschede & Zonen Grafisch CARRIER EQUIPPED WITH A SECURITY ELEMENT.
WO1993025038A1 (en) * 1992-05-29 1993-12-09 Ecole Polytechnique Federale De Lausanne (Epfl) Method for the marking of documents
NL9201701A (en) * 1992-10-01 1994-05-02 Enschede & Zonen Grafisch Security system to detect photocopying of e.g. banknotes

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6678392B2 (en) * 1992-07-31 2004-01-13 Digimarc Corporation Method for encoding auxiliary data within a source signal
WO1997001832A1 (en) * 1995-06-27 1997-01-16 Mikoh Technology Limited A method of reproducing information
US6094722A (en) * 1997-01-24 2000-07-25 Nokia Technology Gmbh Hiding a authentication code in an electric signal
EP0855829A2 (en) * 1997-01-24 1998-07-29 NOKIA TECHNOLOGY GmbH Hiding an authentication code in an electric signal
EP0855829A3 (en) * 1997-01-24 1998-11-18 NOKIA TECHNOLOGY GmbH Hiding an authentication code in an electric signal
NL1006937C2 (en) * 1997-09-04 1999-03-05 Oce Tech Bv Resolution increase by synthesis of scan signals.
US6285803B1 (en) 1997-09-04 2001-09-04 Océ-Technologies B.V. Method and apparatus for resolution enhancement by synthesis of scan signals
EP0902588A1 (en) * 1997-09-04 1999-03-17 Océ-Technologies B.V. Resolution enhancement by synthesis of scan signals
US6351537B1 (en) 1998-10-05 2002-02-26 3M Innovative Properties Company Verifiable holographic article
NL1017173C2 (en) 2001-01-23 2002-08-14 Joh Enschedu B V Security image with double band encryption.
US7027613B2 (en) * 2001-01-23 2006-04-11 Koninklijke Joh. Enschede B.V. Digital security image provided with double-banded coding
EP1435547A1 (en) * 2001-10-11 2004-07-07 Dai Nippon Printing Co., Ltd. Optical structure body for authentication, recording medium for authentication, and confirmation method
EP1435547A4 (en) * 2001-10-11 2007-01-24 Dainippon Printing Co Ltd Optical structure body for authentication, recording medium for authentication, and confirmation method
US7885481B2 (en) 2001-10-11 2011-02-08 Dai Nippon Printing Co., Ltd. Authenticity proving optical structure, authenticating proof recording medium and authenticity certifying method

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